The issue of paramilitary "on-the-runs" has to be resolved, Prime Minister Tony Blair has said.
Mr Blair was speaking at his monthly news conference
It was not just Sinn Fein's concerns that needed to be addressed, he said at his monthly news conference.
All NI political parties have said the controversial "on-the-run" legislation should be scrapped.
However, the Northern Ireland Office has said there is no other vehicle for dealing with the issue of paramilitary fugitives.
Mr Blair said: "The reason we are doing on-the-runs is perfectly simple.
"It is because it is difficult to justify a situation where you have people who were convicted of serious crimes, but as part of the Good Friday Agreement they committed those crimes before April 1998 and they walk free.
"It is very difficult in those circumstances to say that people who were not convicted, but may be charged if they come back in the jurisdiction, should then go to prison for the full term."
Mr Blair also said he believed it would be helpful to reveal more facts about the collapse of the "Stormontgate case", but was still taking legal advice on the correct way to proceed.
The Ulster Unionist Party has said the government should scrap the legislation and not agree to any Sinn Fein proposed changes.
Sinn Fein has said it also wanted the bill scrapped after saying that allowing anyone involved in Troubles-related crime to avoid prison was not what they had agreed.
'Withdraw the legislation'
DUP deputy leader Peter Robinson said there was now no reason for the government to proceed with the "obnoxious and obscene" bill.
The plans cover up to 150 people wanted for crimes committed before 1998.
They would have their cases heard by a special tribunal and, if found guilty, would be freed on licence without having to go to jail.
On Wednesday, the Police Federation for Northern Ireland urged the prime minister to "take Sinn Fein at its word" and withdraw the legislation.
Sir Reg Empey said he wanted the bill scrapped
Federation Chairman Irwin Montgomery said: "Now is the opportunity to do the right thing - even if it is for the wrong reason of Sinn Fein hypocrisy in not wanting the legislation to apply to military or police personnel."
The proposed law would set up a two-stage process. First someone who will be known as the certification officer will decide if someone is eligible for the scheme.
This could be a paramilitary on-the-run, someone living in Northern Ireland who is charged with an offence before 1998 or a member of the security forces accused of an offence committed when they were combating terrorism.
The case would then go to a special tribunal, consisting of a retired judge sitting without a jury. The tribunal would have all the normal powers of the Crown Court but accused would not have to appear for their trial.
If found guilty they would get a criminal record but would be freed on licence. They would have to provide fingerprints and DNA samples to be granted their licence.
The scheme will be temporary but a precise cut-off period is not specified in the bill - instead its expiry is linked to the lifetime of the chief constable's historic cases review team, which is looking at unsolved murders during the Troubles.